In communications systems, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications system is deployed.
For example, one example of applications available in some communications system is group communications services. In general terms, group communication requires that the same information is delivered to multiple clients. These clients may be located at different locations. If many clients are located within the same area, multicast or broadcast based transmission using e.g. Multicast-Broadcast Multimedia Services (MBMS) is efficient.
In group communication systems (e.g. Push-To-Talk (PTT) systems) a floor control function is essential. The floor control function gives the clients the ability to request certain capacity of shared resources used to transmit media to other clients in the group communication system. In order to efficiently use a floor control function there is a need for a floor arbitrator, which at every moment decides which client is allowed to transmit media. The floor control process starts with a client that wish to transmit media sends a floor request message to the floor arbitrator. If there are available resources the floor arbitrator grants the client the right to transmit by the floor arbitrator sending a floor grant message to that client. The floor arbitrator also sends a floor taken message to all clients that have announced interest in participating, and thus exchanging media, in the specific communication group.
In current group communications system being served on cellular communications systems the floor control signaling is typically transmitted together with the media on a specific media bearer. This means that the floor control signaling and the media are transmitted with the same quality of service (QoS). The floor control signaling is sensitive for packet loss. A lost floor control signal can result in that a client does not know when to start to transmit media or that a receiving client does not know who is currently granted the right to transmit media. Correct delivery of the floor control message may thus be regarded as critical. Typically the target is to keep packet loss below 10−6 for control signaling. On the other hand, occasional lost media (e.g. voice) packets will hardly be noticed by the receiving clients. The delivery of the media packets may accept a certain level of packet loss; typically the target is to keep packet loss below 10−2.
When using MBMS to broadcast media in a group communications system, the transmitting client use unicast to transmit the media to the group communications system, and a control node in the group communications system use broadcast to send the media to all receiving clients. There is no uplink bearer available to report lost packets and request retransmissions for the receiving clients. Due to this the modulation and coding of the media transmission (including the floor control signaling) over the air must be robust enough to achieve acceptable QoS. Hence, it is the floor control signaling that sets the requirements on the modulation and coding of the transmission.
In view of the above, the QoS requirements are different for control signaling and media. The encoding of the media and floor control signaling is chosen based on the QoS requirements on floor control signaling, which means that the media is transmitted with a more robust encoding than needed. This leads to inefficient use of MBMS resources as well as radio resources. Another issue is that the clients may need to listen to quite a large MBMS bearer, or several bearers, to capture media from all groups it is affiliated to. This is battery consuming.
Hence, there is still a need for an improved utilization of available network resources for efficient group communications.